| 摘要 |
PURPOSE:To obtain an unequally thick steel pipe having excellent quality by subjecting the steel pipe having parts different in the thickness and outside diameter to a uniform heat treatment in an integrally formed pipe body by means of a heating coil having a specific inside diameter and cooling mechanism. CONSTITUTION:The steel pipe 1 having a thick walled part 1b or 1 and large diameter part at the pipe end, etc. is conveyed 10 and heated 4, by which said pipe is heat treated and at the same time the pipe is cooled by cooling rings 5, 5a on the inside and outside surfaces in the stage of subjecting the pipe 1 to the heating treatment. The preheating coils 3 is advanced adequetely in the conveying direction of the pipe 1 at the same speed as the speed of said coil to preheat only the thick walled part 1b of the pipe 1 by following up thereto. Only the part 1b is cooled by auxiliary cooling rings 5, 5a on the inside and outside when said part passes said rings. Conveying rollers 10 and movable restraining rollers 2, 9 open above and below and convey the pipe 1 during passage of the thick walled part 1b. The coil 3 is used to heat the pipe by as much as the temp. difference DELTAT between the part 1b and the part 1a and the temp. difference DELTAT is determined by the equation when the inside diameter and heating temp. of the coil 4 are determined. |
